The operating condition of a charge storage system which is included in a vehicle, such as, for example, an automobile, truck, aircraft or powerboat, may be determined by evaluating the battery percent charge level, the battery health and/or the charging system health. Alternatively, the electrolyte specific gravity of a battery may be measured for purposes of determining the charge level.
The electrolyte specific gravity of an unsealed battery is typically determined by performing measurements directly at the cells of the battery using a conventional hydrometer float. Such measurements are very time consuming and also potentially hazardous due to the highly volatile gases that often escape from the battery cells.
The typical display on a hydrometer provides a specific gravity reading that is accurate to approximately 10 percent. Further, before a specific gravity value can be interpreted for determining operating conditions in a charge storage system, the specific gravity value on the display may need to be adjusted to compensate for variations in temperature. As a result, for safety and accuracy reasons, a conventional hydrometer float is not generally used for testing the charge storage system in a vehicle.
It is most common that testing of a vehicle charge storage system is performed by measuring the potential difference at the terminals of a battery in a vehicle. This measurement is typically performed when the battery is in an open circuit condition. The open circuit terminal voltage (OCTV) of a battery may be converted into a battery percent charge level, which provides an indication of battery operating condition. See, detailed discussion below.
Charge storage system testing devices and, specifically battery testing devices, which perform OCTV measurements often require periodic recalibration and typically do not include electronics and displays for providing highly accurate readings of the battery percent charge level for expected values. The battery testing industry, for example, uses battery testing devices which include a programmed microprocessor unit that models the internal resistance and capacitance of the battery from OCTV measurements for purposes of providing an indication of battery internal resistance and charge level. These testing devices, however, are typically too costly or too large in size to allow for practical use by the public.
A need, therefore, exists for an economical, convenient, safe and accurate method and apparatus for determining the charge level and health of vehicle charging system components.